Lavender (Lavandula angustifolia) – Botany, Therapeutic Uses, Constituents, Pharmaco, Adverse Effects

Because lavender oil is contained in a number of liniments and cosmetic creams, there have been studies to determine whether linalool and linalyl acetate are absorbed through the skin. In vitro experiments suggest that both compounds make their way into deeper layers of the skin shortly after topical application. The results indicate that linalool is more readily absorbed through skin than linalyl acetate.

In vivo studies of cutaneous absorption have been conducted with human subjects. Similar to the in vitro findings, these experiments indicate that linalool is absorbed through the intact skin. In one study, topical application of linalool was associated with a fall in blood pressure and skin temperature, suggesting a systemic response to this agent. These subjects did not display any signs of an increase in mood or in feelings of well being, indicating that the quantities absorbed were insufficient to affect the central nervous system. Linalool is detectible in deeper skin layers within an hour of its placement on human skin. These levels declined within one to two hours after linalool was removed from the surface of the skin. Evidence indicating that these compounds penetrate the skin completely is provided by the finding that both linalool and linalyl acetate are detected in blood following topical application of lavender oil.

These data suggest that linalool and linalyl acetate, and perhaps other constituents of lavender oil, are sufficiently lipid soluble to cross the skin and accumulate in the systemic circulation. Assuming they are not rapidly metabolized in the intestine, these results suggest these compounds will readily cross from the gastrointestinal tract into blood when taken orally. It is not possible from these reports, however, to estimate the bioavailability, or fraction of an administered dose of these plant constituents, that will appear systemically, and whether either of these compounds penetrates into the brain in sufficient quantities to modify nervous system activity.

In vitro experiments indicate that linalool is metabolized by human liver enzymes. One of the resultant compounds, 6,7-epoxy-linalool, is thought to contribute to the skin irritation that some experience following the topical application of lavender oil. In vivo studies revealed that linalool was metabolically converted in rats to a number of different compounds following its continuous oral administration. Consumption of linalool increased significantly the levels of certain drug metabolizing enzymes in rat liver. These findings confirmed the results of earlier studies with rats indicating that terpenoids, including linalool, when administered either by aerosol or orally, increase the quantity and activity of drug metabolizing enzymes.

While few in number, these experiments suggest that linalool is extensively metabolized following systemic administration, and that long-term exposure to this lavender oil constituent may modify the rate and extent of metabolism of other agents, including prescription medications. Although these studies are too few in number to draw any definitive conclusions, they raise the possibility that any pharmacological response to lavender oil may be mediated by a metabolite of its chemical constituents, and that continuous consumption of this product could influence the activity of drugs being taken for other indications.